If a JComboBox is used in a second swt shell embedded into a SwingControl
and the JComobBox is using a javax.swing.Popup$HeavyWeightWindow, this
popup window will be moved on top of the primary shell while the second
shell (including the rest of the JComboBox) will be moved in the
background. This only occures if the popup of the JComboBox will be
openend the second time.